Investigation of the acetic acid stress response in Saccharomyces cerevisiae with mutated H3 residues

Replacing Glycerol-3-Phosphate Dehydrogenase with NADH Oxidase: Effects on Glucose Fermentation and Product Formation in Saccharomyces cerevisiae

The NADH/NAD+ balance plays a critical role in regulating cellular and metabolic pathways. In Saccharomyces cerevisiae, glycerol-3-phosphate dehydrogenase (ScGPD) enzymes are essential for NADH homeostasis, glycerol biosynthesis, and osmotic stress adaptation. This study investigates the replacement of ScGPD isoforms with the water-forming NADH oxidase from Lactococcus lactis (LlnoxE) and its effects on 10% glucose fermentation dynamics in minimal medium under microaerobic conditions. We engineered S. cerevisiae strains by individually or sequentially deleting or substituting ScGPD isoforms with LlnoxE, generating strains with varying NADH oxidation levels, fermentation rates, and byproduct formation. The engineered strains exhibited three distinct fermentation profiles: faster strains (∆GPD2 and ∆GPD1,2), five medium-speed strains (native, ∆GPD1, LlnoxE/∆GPD1, LlnoxE/∆GPD2, and LlnoxE with GPD), and three slower strains (LlnoxE/∆GPD1,2, LlnoxE/∆GPD1-∆GPD2, and LlnoxE/∆GPD2-∆GPD1). Increased NADH oxidation correlated strongly with higher acetic acid production, which inhibited cell growth and reduced fermentation speed, especially when glycerol biosynthesis was abolished. For instance, LlnoxE/ΔGPD1 reduced glycerol production by 88% and increased ethanol yield by 6.2%, despite a 9% increase in acetic acid production. This study underscores the importance of NADH oxidation in optimizing fermentation efficiency and metabolic balance in S. cerevisiae strains lacking GPD during glucose fermentation.

Cdc73 is a major regulator of apoptosis-inducing factor 1 expression in Saccharomyces cerevisiae via H3K36 methylation

Apoptosis-inducing factor 1 (AIF1) overexpression is intimately linked to the sensitivity of yeast cells towards hydrogen peroxide or acetic acid. Therefore, studying the mechanism of AIF1 regulation in the cell would provide a significant understanding of the factors guiding yeast apoptosis. In this report, we show the time-dependent induction of AIF1 under hydrogen peroxide stress. Additionally, we find that AIF1 expression in response to hydrogen peroxide is mediated by two transcription factors, Yap5 (DNA binding) and Cdc73 (non-DNA binding). Furthermore, substituting the H3K36 residue with another amino acid significantly abrogates AIF1 expression. However, substituting the lysine (K) in H3K4 or H3K79 with alanine (A) does not affect AIF1 expression level under hydrogen peroxide stress. Altogether, reduced AIF1 expression in cdc73Δ is plausibly due to reduced H3K36me3 levels in the cells.